In order to increase recording capacity of an optical information recording medium, attempts have been made on the optical information recording medium to laminate recording layers into a multi-layered structure. As optical information recording media which have been put into practical use for recording information in a plurality of recording layers, write-once digital versatile disks (DVDs) and write-once Blu-ray discs (registered trademark) are already known. However, these media use a one-photon absorption material in the recording layers, with the result that there is a low layer selectivity for causing only a particular recording layer to react upon recording and further that when a far side recording layer is recorded as viewed from a recording beam radiation side, the recording beam is absorbed by near side recording layers. This disadvantageously results in a large loss of the recording beam.
Accordingly, in recent years, attempts have been made to use a multi-photon absorption reaction for the multilayer optical recording medium, in which a reaction occurs only at a limited region in a depth direction upon irradiation with the recording beam, for the purpose of increasing the layer selectivity upon recording thereby increasing the number of recording layers (see, for example, Patent Literature 1, Patent Literature 2, and Non-patent Literature 1). Multi-photon absorption reaction is a reaction of absorbing photons which takes place when a recording layer is given a plurality of (e.g., two) photons substantially simultaneously. For example, in a two-photon absorption reaction, light is absorbed proportionally to the square of the intensity of the light, so that the reaction takes place only at and around the focal point of a beam and if a recording beam having a wavelength at which no one-photon absorption occurs therein is used, the near side recording layers transmits the recording beam without allowing one-photon absorption to occur therein. This is advantageous to increase the number of recording layers.